The present invention relates to an exhaust nozzle for jet engines. Such a nozzle may be used on business aircraft and for commercial aircraft for optimizing their take-off, climb and cruise performance, as well as for increasing safety in flight and reducing speed at landing.
Variable area exhaust nozzles are known in the art. For example, U.S. Pat. No. 5,221,048, which is incorporated by reference herein, describes a variable exhaust area nozzle comprising a fixed structure having mounted thereon two pivoting half shells that cooperate radially and longitudinally with said fixed structure. The two shells and the fixed structure on which they are mounted form the rear part of the nacelle that encloses the engine. Thus, the two shells and the fixed structure form the exhaust nozzle of the engine. Fluid tightness between the two half shells and the fixed structure is provided by a sealing arrangement. Actuators are used to pivot the shells into any position between their fully opened position and their fully closed position. The variation of the position of the shells provides adjustment of the value of the nozzle exhaust area to that required for optimum performance of the engine. Although adjustment of the position of the two shells provides control over the nozzle exhaust area, it does so without modification of the engine thrust vector angle.
Variable nozzle and thrust vectoring of the exhaust of a jet engine is known. U.S. Pat. No. 4,000,610, which is incorporated by reference herein, discloses an apparatus using a flap downstream of a series of converging-diverging flaps to provide flight maneuver (thrust) vectoring as well as external exhaust expansion control. While the series of flaps are internal to the nozzle, and are adapted to form a convergent-divergent shape, they cooperate with the one flap located downstream of the exhaust nozzle for external expansion control of the exhaust. Convergent-divergent nozzles such as this are typically used on supersonic aircraft such as military aircraft.
Thrust vectoring technology has been successfully demonstrated on tactical military aircraft to provide maneuvering advantages in very low speed, very high angle-of-attack flight regimes. Current research is exploring the benefits of using thrust vectoring to decrease cruise trim drag under high altitude and mid to high speed conditions. This technology has matured to the extent that it is being incorporated into military fighter aircraft.
As far as is known, thrust vectoring has not been used on commercial or business aircraft. Some of the reasons for this are that the technology is typically very complex, and involves many moving parts, which is detrimental to the overall dispatch reliability and operational cost of a business or commercial aircraft. Another reason that thrust vectoring has not been used on commercial or business aircraft is that these aircraft usually have little need for maneuvering agility. Despite the foregoing, the potential for improved safety and increased cruise efficiency that may result from the use of thrust vectoring would make it attractive to the commercial and business aircraft community if a simple thrust vectoring system having a low number of moving parts could be provided.
Thrust vectoring also could provide benefit to commercial and business aircraft by providing improved longitudinal stability. Longitudinal stability is needed due to the fact that aircraft are designed to have an aerodynamic center of pressure (CP) located aft of the aircraft center of gravity (CG). As a result of this arrangement, cruising aircraft inherently have a nose down pitching moment, caused by the CP being aft of the CG. This nose down moment must be offset during flight by a nose up pitching moment created by the horizontal stabilizer. These opposing forces help maintain stability but create drag, which can reduce aircraft efficiency.
Thrust vectoring may be used to assist in the provision of aircraft longitudinal stability and the reduction of overall drag during cruising by placing the exhaust nozzle in a xe2x80x9cnozzle upxe2x80x9d position. When the thrust vector is directed upwards, the vertical component of the thrust vector creates a nose up pitching moment for the aircraft. The nose up pitching moment produced by the thrust vector allows the horizontal stabilizer to be operated at a lower angle-of-attack which reduces the negative lift created by the aircraft horizontal stabilizer and therefore reduces the aircraft drag. Furthermore, integration of the thrust vectoring system into the flight control system assists in providing aircraft longitudinal stability, thus allowing highly efficient reduced-tail designs, which in turn may reduce tail weight and consequently the overall aircraft weight.
Swept wing, T-tailed aircraft tend to suffer a marked nose up pitching moment at aerodynamic stall which can allow the low energy turbulent airflow behind the wing to immerse the tail. This can greatly reduce the effectiveness of the tail in countering the nose up pitching moment. When the nose up pitching moment created by the wing during stall is greater than the nose down pitching moment created by the horizontal tail, recovery from the stall may be impossible. Just as thrust vectoring may be used to assist the tail in providing a nose up pitching moment during cruise, thrust vectoring may be used to assist the tail in providing a nose down pitching moment during stall. All that is required is that the nozzle be placed in a nozzle-down position.
Thrust vectoring may be used further to improve landing performance and decrease or eliminate the need for thrust reversers. Landing performance is predicated on the landing approach being carried out at a generally constant angle-of-attack. At a generally constant angle-of-attack, airspeed varies directly with the weight supported by the wing i.e., aircraft weight. Required runway length is a function of aircraft weight, approach speed, and aircraft braking ability. As the ability to increase runway length and decrease aircraft weight is somewhat limited, control over aircraft stopping distance is largely exercised through control of braking ability.
Most aircraft, at landing, use thrust reversers for deceleration. However, these reversers, which are used at landing for about 30 seconds, can produce catastrophic events if an inadvertent deployment occurs during flight. Thrust reversers are required primarily on a wet or icy runway, because of the high speeds at which aircraft are required to land. If the landing speed of aircraft could be reduced, the need for thrust reversers could potentially be avoided. Thus, there is a need for aircraft engines that enable the landing speed of an aircraft to be reduced.
One such method of reducing aircraft landing speed may be to provide an engine that assists in lift through adjustment of the engine thrust vector. By placing the exhaust nozzle in a nozzle-down position, some portion of the aircraft weight may be supported directly by the vertical component of the vectored thrust thus reducing the weight supported by the wing. This support of the aircraft by a vertical component of thrust vectoring could be used to reduce approach speeds, and thus reduce landing speeds. Reduced landing speeds could decrease or eliminate the need for thrust reversers on the aircraft. Induced drag would be decreased and angle-of-attack reduced.
Thrust vectoring may also be used to assist in maneuvering an aircraft. For fuselage mounted engines in particular, the left engine exhaust nozzle can be controlled to an asymmetrical vectoring position (nozzle up for example) while the exhaust nozzle of the right engine is controlled to the opposite direction (nozzle down position), and vice versa. Such thrust vectoring may be used to generate a rolling moment to the aircraft. If the thrust vectoring system is integrated into the flight control and/or auto-flight systems, then an independent backup flight control system is available to the flight crew. Furthermore, if power for the thrust vectoring system is different from the flight control system i.e., electric vs. hydraulic, then an additional level of redundancy is created, which further increases the overall safety of the aircraft. On a multi-engine aircraft, pitch axis thrust vectoring can create aircraft movement about the pitch (symmetrical vectoring) and roll (asymmetrical vectoring) axes.
The system described and claimed herein, may provide the foregoing advantages and is an improvement over the systems disclosed in U.S. Pat. Nos. 5,221,048 and 4,000,610. As compared with these prior systems, various embodiments of the present invention require fewer moving parts, are not complex, and are relatively inexpensive, while allowing for variation of both the nozzle exhaust area and the engine thrust vector angle. This permits both exhaust area and thrust vector angle to be adjusted for optimized engine performance during different flight conditions.
It is therefore an object of the present invention to provide a jet engine nozzle with thrust vectoring capabilities.
It is another object of the present invention to provide a jet engine nozzle with variable exhaust area capabilities.
It is yet another object of the present invention to provide a jet engine nozzle with both thrust vectoring and variable exhaust area capabilities.
It is still another object of the present invention to provide a jet engine nozzle with thrust vectoring and variable exhaust area capabilities that has fewer moving parts than previously known nozzles.
It is yet another object of the present invention to provide a jet engine nozzle with thrust vectoring and variable exhaust area capabilities that is less expensive to make or maintain than previously known nozzles.
It is still yet another object of the present invention to provide a jet engine nozzle that improves the longitudinal stability of an aircraft.
It is still yet another object of the present invention to provide a jet engine nozzle that reduces the required landing speed of an aircraft.
It is still yet another object of the present invention to provide a jet engine nozzle that may be used to pitch and/or roll an aircraft.
Other objects, characteristics and advantages will become apparent from the following description in reference to the accompanying drawings.
The invention comprises a variable area exhaust nozzle with variable thrust vector angle for one or more jet engines having shells pivotally mounted on a fixed structure called jet pipe with two extending arms. The jet pipe with its extending arms and the pivoting shells form the exhaust nozzle of the engine. The shells are pivoted and controlled by actuator means which pivot the shells either to a symmetrical configuration for changing the value of the exhaust area of the nozzle or unsymmetrical configuration for changing the value of the angle of the thrust vector relative to the engine centerline. The actuator can be hydraulic, electric or pneumatic or other extendible actuators to provide controlled pivoting of the shells. In one embodiment there is a single actuator per shell, said actuator being connected to the jet pipe and the shell to provide controlled pivoting of said shell; in this embodiment, said actuator is located substantially in the vicinity of the plane of symmetry of said shell. In another embodiment there are dual actuators on each side of the jet pipe to provide controlled pivoting of the shells. The invention includes a method for adapting an exhaust nozzle mounted on the aft portion of a nacelle which wraps a turbo-fan engine, by varying the value of the exit area or by changing the thrust vector angle of said exhaust nozzle during a flight segment.
The method also includes varying the value of the exhaust area of the nozzle and the thrust vector angle on opposite side engines, whether said engines are aircraft wings mounted or fuselage mounted.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only, and are not restrictive of the invention as claimed. The accompanying drawings, which are incorporated herein by reference and which constitute a part of this specification, illustrate certain embodiments of the invention, and together with the detailed description serve to explain the principles of the present invention.